Field of the Invention
The invention relates to a support assembly, in particular for a motor vehicle, for absorbing kinetic energy during an impact, including a supporting structure and a deformation element for oblique introduction of force. The deformation element is supported at least at one end at a support at the supporting structure and has a honeycomb matrix body with a longitudinal axis and cavities formed by walls. The invention also relates to a vehicle bumper system and a method of producing a support assembly.
Deformation elements for absorbing kinetic energy are used in various areas of engineering. One particular area of application for elements of that kind is in motor vehicles. Technical and safety standards require that, in the case of minor impacts, impact energy should be absorbed in an essentially elastic manner by corresponding elements. In the case of more severe impacts, e.g. in the case of accidents, the kinetic energy should be absorbed by elements and converted into deformation of the latter. Thus, for example, the prior art includes deformation elements which are used for longitudinal members of a vehicle and which remain undamaged in the event of an impact up to 4 km/h and, in the case of an impact up to 15 km/h, absorb the entire kinetic energy and convert it into deformation. In general, such deformation elements are integrated into the longitudinal member to form a unitary supporting structure, with the result that the entire longitudinal member has to be replaced in the event of damage. The requirement that essentially the entire kinetic energy should be absorbed by the deformation elements without a significant proportion of that deformation energy being transmitted to the other structures of a motor vehicle, is one that must also be satisfied with a view to increasing the survival chances of people in vehicles that are involved in an accident.
Honeycomb structures are used in many different ways for various applications in engineering. For example, honeycomb structures are used in the construction of aircraft, where requirements for lightweight construction and high strength, in particular, are important. Honeycomb structures are also known from areas where it is not so much the strength of such a honeycomb structure as increasing the surface area which is important. For example, they are used in the case of catalyst substrates in the exhaust system of a motor vehicle for removing the noxious exhaust components that remain in the exhaust after combustion in the engine.
German Utility Model G 89 00 467 U1, European Patent Application 0 389 750 A1, UK Patent Application GB 2 029 720 A, German Published, Non-Prosecuted Patent Application DE 40 24 942 A1, German Patent DE 38 09 490 C1 and German Published, Non-Prosecuted Patent Application DE 44 45 557 A1, corresponding to U.S. application Ser. No. 08/879,594, filed Jun. 20, 1997, now U.S. Pat. No. 6,334,981, have disclosed various configurations and structures for honeycomb bodies. In general, those honeycomb bodies that have been described are used to improve flow characteristics in the channels of the matrix body, which are constructed as flow channels, in order to obtain improved chemical reactions. The jacketing configurations surrounding the actual matrix body are used to absorb high thermal loads, to which catalyst substrates of that kind are exposed in the exhaust system of a motor vehicle.
German Published, Non-Prosecuted Patent Application DE 196 50 647 A1 has disclosed a deformation element for a motor vehicle, in which a honeycomb body that is known per se and disposed in a jacketing tube is used as a deformation element.
The disadvantage of the known deformation elements is that they are either integrated completely into the supporting structures, necessitating replacement of the entire supporting structure in the event of damage or, where deformation elements with a honeycomb structure are used, a steep initial rise in a curve describing a deformation force/deformation path profile (F,s profile) occurs relatively quickly if high kinetic energy is introduced. That can lead to high deformation forces that occur being transmitted directly into the supporting structure and the latter being deformed plastically as a result.
It is accordingly an object of the invention to provide a support assembly having a supporting structure and a deformation element for oblique introduction of force and absorption of kinetic energy, which ensures a desired F,s profile, in accordance with a respective application-specific construction, as compared with a conventional deformation element, as well as a vehicle bumper system and a method of producing a support assembly, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a support assembly, in particular for a motor vehicle, for absorbing kinetic energy during an impact, comprising a supporting structure having a support; and a deformation element having a honeycomb matrix body with a longitudinal axis and walls forming cavities, the walls having a main direction of extension, the deformation element having at least one end supported at the support of the supporting structure, and the deformation element secured at the supporting structure for introducing at least some forces developed during an impact into the walls at an angle to the main direction of extension.
In accordance with another feature of the invention, the matrix body is made up of at least one at least partially structured layer of sheet metal by looping, winding or stacking, preferably into a cylindrical form. A honeycomb matrix body produced in this way is made, for example, from a combination of corrugated and essentially smooth layers of sheet metal, which are disposed alternately to one another. This gives rise within the matrix body to cavities, which are bounded by the walls formed by the layers of sheet metal. The walls extend essentially in the direction of the longitudinal axis of the matrix body. The cavities are preferably constructed as channels, which extend coaxially to the longitudinal axis of the matrix body, for example. If a deformation element with a matrix body of this kind is secured on the supporting structure in such a way that the forces introduced during an impact act essentially in the direction of the walls, the deformation energy is absorbed inter alia by the fact that the walls are subjected to a buckling load, i.e. are compressed. That results in a relatively sharp rise in the deformation force/deformation path profile (F,s profile) immediately after the introduction of the kinetic energy. This steep initial rise or initial peak in the F,s profile has the effect of introducing relatively high deformation forces into the supporting structure through the deformation element before the latter is deformed and thereby absorbing kinetic energy. As a result, it is possible for the supporting structure to undergo plastic deformations due to the peaks in the deformation force. However, this is to be avoided since, in keeping with its function, the deformation element is intended to absorb the kinetic energy and prevent the supporting structure from undergoing plastic deformation.
According to the invention, provision is therefore made for the deformation element to be constructed or disposed relative to the supporting structure in such a way that the forces developed during an impact are introduced at an angle to the main direction of extension of the walls. That direction is defined in relation to the longitudinal axis. It is ensured that the walls can be deformed into the cavities more easily, in particular at the onset of deformation, by introducing the forces obliquely in this way. As a result, the initial peak in the F,s profile is at least greatly reduced. At least the initial region of the F,s profile can thus be influenced in a specifically targeted manner to yield an improvement in the absorption of kinetic energy being introduced, through the use of a deformation element of this kind according to the invention.
According to one exemplary embodiment of the invention, the main direction of extension of the layers of sheet metal forming the walls is disposed at an angle to the longitudinal axis. This can be achieved, for example, by winding the individual structured layers of sheet metal obliquely. In accordance with an added feature of the invention, if the main direction of extension of the walls forms an angle with the longitudinal axis, the deformation element can be secured on the supporting structure in such a way that the longitudinal axis is disposed essentially perpendicular to the support on the supporting structure.
However, it is also possible to use a conventional matrix body, in which the main direction of extension of the walls is essentially coaxial with the longitudinal axis of the matrix body. In accordance with an additional feature of the invention, the matrix body is secured on the supporting structure in such a way that its longitudinal axis is disposed at an angle, that is not a right angle, to the support on the supporting structure.
In accordance with yet another feature of the invention, the layer or layers of sheet metal are wound, looped or stacked in such a way that a conical or frustoconical matrix body is formed. A conical or frustoconical matrix body of this kind is preferably disposed on the supporting structure in such a way that its longitudinal axis is essentially perpendicular to the support on the supporting structure, thereby likewise achieving an oblique introduction of forces relative to the main direction of extension of the walls.
In accordance with yet a further feature of the invention, there is provided a multiplicity of predetermined deformation points disposed in the layers of sheet metal forming the walls. As a result, the F,s profile of the deformation element is constant at least in certain sections or at least in one section. One significant advantage of an F,s profile that is constant at least in certain sections is that, when kinetic energy is introduced into the deformation element, the latter is deformed uniformly and transmission of the absorbed kinetic energy to the supporting structure is very largely avoided.
In accordance with yet an added feature of the invention, the predetermined deformation points in the walls of the matrix body are provided and constructed in such a way that the F,s profile of the deformation element is made to rise progressively, at least in one section or in certain sections. At the same time, the rise in the F,s profile is configured in such a way that, at the end of the deformation travel, at which the so-called residual block length of the deformation element is reached, the maximum force is preferably below a value at which the supporting structure undergoes plastic deformation.
In accordance with another feature of the invention, the cavities of the matrix body are constructed as channels, so that as a result the matrix body has a multiplicity of channels. Layers of sheet metal having a thickness of 0.02 mm to 0.2 mm are preferably used, and the matrix body preferably has a cell density of 50 to 600 cpsi (cells per square inch). When aluminum sheets are used, a thickness of 0.05 to 0.2 mm is preferred and, in the case of steel sheets, in particular deep-drawing steel, a thickness of 0.02 to 0.15 mm is preferred.
In accordance with yet an additional feature of the invention, the deformation element is provided, at least at one end at which there is a support on the supporting structure, with a perforated plate having at least one hole. The at least one hole in the perforated plate is dimensioned in such a way that parts of the matrix body situated in the area of the hole can be displaced into the hole or through the hole in the direction of the deformation if a high kinetic energy is introduced. The displacement of parts of the matrix body which are situated in the area of the hole through the hole or into the hole in the direction of the main deformation occurs even before the residual block length is reached. Shearing off of individual layers of sheet metal in the region of the edge of the holes and compression of the layers of sheet metal occur essentially simultaneously, with the result that parts of the matrix body enter or pass through the hole. Once the residual block length has been reached, the deformation element still has a certain residual porosity. The matrix body preferably has a jacketing configuration which is constructed in such a way that it folds uniformly, preferably in the form of rings, during deformation.
One of the significant advantages of this construction according to the invention, as compared with a construction having an end plate without a hole, i.e. not a perforated plate, is that, when the maximum deformation travel is reached, the resulting residual block length is reduced and, as a result, the maximum deformation travel is increased. That is because the at least one hole in the perforated plate is dimensioned in such a way that, under the action of compressive and shearing forces, parts of the matrix body which are disposed in the area of the hole are pushed into the hole or even out of the hole when further kinetic energy is introduced into the deformation element. As a result, the steep rise that occurs in the F,s profile when the residual block length is reached, i.e. the rear region of the F""s profile, such as that which occurs in the case of a deformation element with a closed cover plate disposed at its end or where the end of that deformation element rests fully against the support of the supporting structure, is pushed back further, i.e. shifted to the right in the F,s profile.
In accordance with again another feature of the invention, the perforated plate has a plurality of holes, which can be distributed uniformly or nonuniformly in the surface of the perforated plate. In this configuration, the size of the holes is preferably such that those parts of the matrix body which are disposed in the area of the holes can essentially push into or through all of the holes under the action of the deformation and shearing forces when kinetic energy is introduced.
In accordance with again a further feature of the invention, the edge of the respective hole is constructed in such a way that it extends over as many layers of sheet metal as possible. This is necessary to ensure that the layers of sheet metal of the matrix body which are situated in the area of the edge of the hole are sheared off through the use of shearing forces instead of individual parts of the matrix body being displaced through the hole in a telescope-manner without shearing taking place. In accordance with again an added feature of the invention, the holes are preferably disposed in the outer area of the perforated plate. This has the advantage of achieving an interaction between the jacketing configuration and the matrix body during deformation. Since parts of the matrix body can be displaced through the holes in the perforated plate in the direction of the deformation, in particular in the outer area, the cavity which is thus created can be compressed by the lateral force imposed by the jacketing configuration during deformation. A shortening of the residual block length can thereby be achieved.
In accordance with again an additional feature of the invention, about 20 to 80%, preferably 40 to 60%, of the total area of the perforated plate is formed by holes. This ensures sufficient space through which or into which sheared-off parts of the matrix body can pass through the perforated plate when a high kinetic energy is introduced. The edges of the holes are preferably constructed in such a way that they extend over at least ten layers of sheet metal. If a single hole is provided and the diameter of the matrix body is 90 mm, for example, the diameter of the hole can be about 55 mm. However, the corresponding holes in the perforated plate can differ therefrom with regard to their configuration and size, depending on the application and the desired F,s profile.
In accordance with still another feature of the invention, the perforated plate is integrated through the use of its edge into the support of the supporting structure. On one hand, this ensures that adequate supporting forces are available and, on the other hand, that a high deformation energy can be introduced.
In accordance with still a further feature of the invention, the jacketing configuration is constructed in the form of a plurality of separate jacketing rings or in the form of a continuous jacketing tube with predetermined buckling points. Depending on the construction of the jacketing configuration, the kinetic energy is absorbed both by the matrix body and the jacketing configuration to a greater or lesser extent. The deformation element is supported or held in the supporting structure at one or both ends in such a way that the kinetic energy to be absorbed can be introduced essentially in the longitudinal direction of the deformation element. By virtue of the construction of the honeycomb matrix body with a multiplicity of channels, the formation of a perforated plate with holes of defined dimensions, the thicknesses and types of material etc., there is great flexibility of layout with regard to the achievement of specific dimensioning of the deformation element according to the invention for particular applications. It is thus possible to achieve a desired F,s profile.
If the deformation element has a tubular construction, it is also referred to as a deformation tube (DEFO tube). In principle, the deformation element is constructed in such a way, by appropriate shaping and selection of the above-mentioned parameters, that a maximum deformation travel is achieved for the given dimensions of the component. This is possible, for example, by folding or compressing the jacketing configuration and/or the matrix to absorb the kinetic energy.
Another advantage of such a deformation element according to the invention is that ease of fitting and removal can be achieved through the use of a special construction of the deformation element including its jacketing configuration. The respective construction of the jacketing configuration and of the respective honeycomb structure of the matrix body furthermore serves to enable load-bearing properties to be achieved. Those properties must be ensured if the deformation element according to the invention is to be integrated or embedded into frame or supporting structures, making it possible to transmit loads at which the deformation element is capable of absorbing even the kinetic energy that occurs during impact loading. A suitable choice of material will furthermore enable corrosion-resistant material to be used for the deformation element according to the invention if the respective application demands it. However, it is also possible to sacrifice corrosion-resistant materials for reasons of cost and to provide the materials used for the element according to the invention with an anti-corrosion coating that is known per se.
The respective F,s profile can thus be influenced in a specifically targeted manner through the use of the construction both of the matrix and of the jacketing configuration. An essentially smooth jacketing configuration, for example, helps to provide a high load-bearing capacity. If the jacketing configuration is constructed as expanded metal or has holes or discontinuities, for example, a maximum deformation travel can be achieved. The specific deformation behavior of the deformation element can likewise be influenced in a specifically targeted manner by placing beads, notches, grooves, etc. in the jacketing configuration. The strength can furthermore be influenced through the use of the respective thickness of the jacketing configuration and the material chosen for the jacketing configuration.
It is also possible to use the construction of the matrix body to influence the deformation behavior in a specifically targeted manner through the use of layers of sheet metal with transverse structures, for example. A maximum deformation travel can be achieved if the individual layers of sheet metal have holes, slots or longitudinal structures. The strength and weight of the deformation element according to the invention can furthermore be influenced in a specifically targeted manner through the use of its cell density, sheet thickness and method of winding of the matrix body. This can also be achieved, for example, through the use of oblique corrugations by using a cross-wound configuration. It is furthermore also possible to construct the matrix body in such a way that radial rigidity is reduced at the edge.
In accordance with still an added feature of the invention, the jacketing configuration has a bead or a plurality of beads disposed essentially transversely to the channels of the matrix. The advantage of these beads is that, if the kinetic energy is introduced essentially in the longitudinal direction of the deformation element, the beads on one hand have a certain initial elasticity and on the other hand represent points at which the jacket initially absorbs kinetic energy. The sides of each bead are folded up against one another in the presence of corresponding deformation forces before the essentially smooth areas of the jacket between the beads are subjected to direct further deformation. These beads thus represent predetermined deformation points. Depending on the application and the level of kinetic energy to be absorbed, the jacketing configuration of the matrix body has a thickness of 0.3 mm to 2.0 mm. However, greater thicknesses are possible and appropriate for very high levels of kinetic energy to be absorbed. When aluminum is used as a jacket, a thickness of 0.5 to 2.0 mm is preferred, and a thickness of 0.03 to 1.5 mm is preferred in the case of steel, in particular deep-drawing steel.
In accordance with still an additional feature of the invention, the matrix body includes, in a manner known per se, packed flat layers of sheet metal or an essentially cylindrically wound assembly formed by a spiral, an involute shape or S shape, for instance. The individual layers of sheet metal resting upon one another in the assembly can, but need not, be brazed together in the areas of contact.
In accordance with another feature of the invention, the cell density of the matrix body is varied from section to section in the longitudinal direction. This is achieved, for example, by inserting additional layers of sheet metal with shallower corrugations or more widely spaced corrugations than in the corresponding adjacent section between essentially smooth layers of sheet metal. The smooth layers of sheet metal of the section with the lowest cell density are preferably disposed in such a way as to be continuous in the longitudinal direction of the matrix. It is also possible to vary the cell density of the matrix in the radial direction by winding up a layer of sheet metal with a corrugation frequency that increases continuously in one direction to form an essentially cylindrical honeycomb structure, for example. Varying the cell density furthermore has the advantage of providing intersecting boundary surfaces between channel walls within the honeycomb body. When deformation occurs, not only compression but also a shearing force occurs at these points since the metal sheets cut or tear one another. In accordance with a further feature of the invention, a similar effect can also be achieved if two or more honeycomb bodies are disposed in series, more specifically in such a way that as many layers of sheet metal from both bodies as possible cross at their adjoining ends. This can be achieved by using honeycomb bodies with a different winding direction, for example. This makes it possible for the configuration to absorb even more deformation energy with the same volume.
In accordance with an added feature of the invention, the layers of sheet metal of the matrix have bead-like structures essentially transversely to the direction of the channels. These structures are also referred to as transverse structures. These transverse structures serve to ensure that when a sufficiently high kinetic energy is introduced, deformation within the matrix body starts initially at the transverse structures so that in this way as uniform as possible absorption of the kinetic energy by the matrix body or by the matrix body and the jacketing configuration is ensured. In accordance with an additional feature of the invention, these transverse structures are preferably disposed at a spacing of from 2 mm to 20 mm.
In accordance with yet another feature of the invention, the layers of sheet metal of the matrix body forming the channels have laterally offset channel sections within the channels. Those channel sections are also referred to as longitudinal structures. These longitudinal structures thus do not provide continuous channels but rather discontinuous channels, with the result that the matrix body has a structure within it corresponding to a plate-fin structure, as is used inter alia for heat exchangers. The advantage of these longitudinal structures is that the kinetic energy-absorbing properties of the deformation element according to the invention can additionally be influenced in a specifically targeted manner through the use of the length of the channel sections that are offset section by section. This provides a further parameter for influencing the F,s profile to suit the specific application.
In accordance with yet a further feature of the invention, the corrugations of the layers of sheet metal have a curved or herringbone configuration or a combination of the two. Through the use of such curved corrugations or herringbone-configuration corrugations on the layers of sheet metal, it is possible to achieve a specific distribution of the deformation-inducing forces introduced into the interior of the matrix body, thereby likewise enabling the F,s profile to be influenced in an application-specific manner.
In accordance with yet an additional feature of the invention, the matrix body or its channels are filled with a foamed material. The foamed material is preferably a foamed plastic, in particular a corrosion-inhibiting foamed plastic. On one hand, this prevents corrosion from occurring within the matrix and the jacketing configuration if stainless steel is not used. For example, such corrosion potentially has a disadvantageous effect on the deformation properties. On the other hand, it is also possible, through the selection of an appropriate foamed plastic with defined properties, to influence the absorption capacity for kinetic energy in the element in a specifically targeted manner. As a result, it is also possible to influence the F,s profile by introducing a foamed material.
In accordance with again another feature of the invention, with a view to a maximum deformation travel to be achieved relative to a defined overall length, the deformation element is constructed in such a way, with regard to its deformation behavior, that the maximum deformation travel is from about 60 to 200 mm. The deformation travel can also be less than or greater than the range stated, depending on the application.
With the objects of the invention in view, there is also provided a vehicle bumper system for absorbing kinetic energy, comprising a supporting structure having a support; and a deformation element having a honeycomb matrix body, in particular a metallic honeycomb matrix body, with a longitudinal axis and walls forming cavities, the walls having a main direction of extension, the deformation element having at least one end supported at the support of the supporting structure, and the deformation element secured at the supporting structure for introducing at least some forces developed during an impact into the walls at an angle to the main direction of extension.
In this case, the deformation element according to the invention is dimensioned in such a way that the initial peak in the F,s profile is at least greatly reduced. This avoids a situation where large forces are transmitted to the supporting structure at the beginning of the introduction of kinetic energy into the deformation element, thus very largely excluding damage to the supporting structure.
It is thus possible to introduce even very high levels of kinetic energy without damaging the supporting structure. The improved deformation potential of such a deformation element thus resides in reducing the residual block length. This makes it possible to construct the deformation element according to the invention as an assembly component that can be removed with little outlay when kinetic energy has been introduced and converted into deformation and can be replaced by a new element. This not only increases safety in ram-type accidents and impacts but also makes a vehicle bumper system fitted with a deformation element according to the invention easier to repair.
With the objects of the invention in view, there is additionally provided a method for producing such a support assembly, which comprises producing an uncompressed deformation element having an F,s diagram with an initial peak having a maximum; and then subjecting the deformation element to an initial compression with a deformation force greater than the maximum of the initial peak in the F,s diagram of the uncompressed deformation element.
There is accordingly another way of producing a deformation element with the desired properties, namely without a significant initial peak in the F,s profile, without extensive structural modifications to conventional honeycomb bodies. All that is required is to subject any honeycomb body produced in a manner that is known per se to a controlled initial compression. It is possible for this to be carried out during production or at the location of installation. The force employed for this purpose should be greater than the maximum force in the initial peak of the F,s profile of the as yet uncompressed honeycomb body. The initial peak is thus traversed and eliminated before the deformation element is used for the first time. This gives rise to a honeycomb body that is already somewhat deformed and undergoes oblique introduction of force into its walls in accordance with the invention.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a support assembly having a supporting structure and a deformation element for oblique introduction of force, a vehicle bumper system and a method of producing a support assembly, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.